Question: Solve for $x$ and $y$ using substitution. ${-4x+5y = -9}$ ${x = y+1}$
Answer: Since $x$ has already been solved for, substitute $y+1$ for $x$ in the first equation. ${-4}{(y+1)}{+ 5y = -9}$ Simplify and solve for $y$ $-4y-4 + 5y = -9$ $y-4 = -9$ $y-4{+4} = -9{+4}$ ${y = -5}$ Now that you know ${y = -5}$ , plug it back into $\thinspace {x = y+1}\thinspace$ to find $x$ ${x = }{(-5)}{ + 1}$ ${x = -4}$ You can also plug ${y = -5}$ into $\thinspace {-4x+5y = -9}\thinspace$ and get the same answer for $x$ : ${-4x + 5}{(-5)}{= -9}$ ${x = -4}$